1. Technical Field
The present invention relates in general to an improved device and method for creating an air bearing. More particularly, the present invention relates to movements with reduced friction between objects.
2. Description of the Prior Art
The movement of objects is bind to loss of energy because of friction. Friction is a force that opposes the motion of an object when the object is in contact with another object or surface. Friction results from two surfaces rubbing against each other or moving relative to one another. It can hinder the motion of an object or prevent an object from moving at all. The strength of frictional force depends on the nature of the surfaces that are in contact and the force pushing them together. This force is usually related to the weight of the object or objects. Usually, the friction between the moving objects of a device, e.g. an engine, turns energy into heat, reducing the device""s efficiency. Friction also makes it difficult to slide a heavy object. Two surfaces in contact also tend to attract one another at the molecular level, forming chemical or physical bonds. These bonds can prevent an object from moving, even when it is pushed. If an object is in motion, these bonds form and release. Making and breaking the bonds takes energy away from the motion of the object.
The normal force is the force the object exerts perpendicular to the surface. In the case of a level surface, the normal force is equal to the weight of the object. If the surface is inclined, only a fraction of the object""s weight pushes directly into the surface, so the normal force is less than the object""s weight.
Different kinds of motion give rise to different types of friction between objects, for example static friction, sliding friction, also called kinetic friction, or rolling friction. While friction allows to convert one form of motion to another, it also converts some energy into heat, noise, and wear and tear on material. Losing energy to these effects often reduces the efficiency of a machine.
Reducing the amount of friction between objects increases the efficiency of the movement. Less friction means less energy lost to heat, noise, and wearing down of material.
Several methods for reducing friction are known. One method involves reducing the roughness of the surfaces in contact. Applying a lubricant to a surface can also reduce friction. Common examples of lubricants are oil and grease. They reduce friction by minimizing the contact between rough surfaces. The lubricant""s particles slide easily against each other and cause far less friction than would occur between the surfaces.
A more efficient way to move an object and to reduce friction is to have an air cushion. Air cushions have a long history. Known are, for example, air-cushion vehicles, also called hovercrafts, crafts that operates above the surface of water or land. Such a vehicle is supported on a cushion of air. The air cushion is provided by a large fan that pushes air downward within a flexible skirt attached to the perimeter of the vehicle. The skirt maintains the cushion by restraining the air. It makes the vehicle appear to be operating only a few inches above the surface. The vehicle is moved forward by propellers mounted above the vehicle or by control of the air exhaust through small openings around the skirt.
In magnetic recording, a head is sliding on an air cushion over a disk in order to avoid the contact between the head and the disk which may lead to wear. This is achieved by the specific construction of the head""s shape. Moreover, several production or assembly lines using airflows or air bearing conveyers for the transport of materials or goods, e.g. wafer. In mechanical engineering compressed air is blown into bearings, so called air bearings, to achieve reduced friction during rotations.
The most of the aforementioned techniques use a flow of air to generate an air cushion or air bearing. This flow might be generated by a fan. In the micromechanical world, systems allowing reduced friction are nearly unknown. This calls for innovative solutions, since it becomes crucial in the near future, when spinning disks, for example, get smaller and smaller entering the micromechanical regime. Thus, it is an object of the present invention to provide a nearly frictionless system for moving objects relative to each other.
In order to achieve the objectives of the present invention, a device comprises a first object and a second object each having an at least partially parallel surface facing each other. The device further comprises an oscillator for creating an oscillation of a medium between the first and second objects to generate an air bearing between the first and second object. Thereby relative movement between the first and second objects is permitted.
A method for creating an air bearing between the first object and the second object each having an at least partially or to some extent parallel surface facing each other is also provided. The method comprising the step of oscillating a medium between the first and second surfaces to generate an air bearing between the first and second objects. Using the device or method, a nearly frictionless movement between the surfaces of the objects can be achieved. Therefore, no lubrication is necessary at all. The invention is particularly well suited for micromechanical applications but is not restricted to them.
In one aspect of the present invention, the device comprises at least a spacer between the first and second object. This is advantageously because then the first object is separated from the second object and the creation of the air bearing can be initiated more easily. When the spacer comprises a cantilever having a contact area with one of the first or second objects or the spacer is a foot, then the advantage occurs that the distance between the first and second object can be exactly defined. This may play a role when several objects are placed on the air bearing. The cantilever can have a tip, then the advantage occurs that the contact area is very small and the forces between the tip and the first or second object can be overcome easily without much power. It is advantageously if many several objects, e.g. robots, have different surfaces, shapes, or weights such that each object starts its movement at a defined resonant frequency. By doing so, individual control of a lot of objects is achievable.
The oscillator for the oscillation of the medium between the first and second object might comprise piezoelectric, capacitance, electromagnetic, or ultrasonic elements. By using the listed elements, the stimulation of the medium to oscillate can be generated efficiently by well-understood techniques. The medium in-between the first and second objects may comprise air, a gas, or a mixture thereof, but also a liquid or a thin liquid might be advantageous for some applications.
It should be noted that not only the medium can be oscillated but also the first and second objects or even a combination thereof. With air bearing is meant that not necessarily air between the first and second object permits relative movement, but also a gas or a liquid or any other suitable medium can be applied in order to reduce the friction between the objects.
If one of the first and second objects comprises an imbalance or unbalance, than an unbalanced movement of one of the first and second objects can be achieved. If the object having the unbalanced movement is encircled by a wall or a tube, than the advantage occurs that this object adjusts itself to a constant rotation. When the first object has a recess for reception of the second object, then the advantage occurs that the second object adjusts or centers itself by the air vibrations. If the second object is a disk or a wheel and its motion is activated by capacitance, magnetic or airflow means, then a high speed motor can be provided.
If the first object encircles at least partly the second object, then the advantage occurs that the device with the first and second object can be operated at different angles. One of the first and second objects is a moving part, also referred to as moving object. Therefore, the moving object can be everything which is useful to move, for example a disk, a tool, a container, a plate, a write/read unit, or a robot.
If the moving object is rotating it appears advantageous if a spindle guides the moving object. Owing the moving object holds its defined position. Also possible is a guide element. For example, a wall or a tube might be applicable that oscillates at its radius. It is also possible to arrange several guide wheels or the like at the circumference of the moving object in order to guide the moving object on a predefined position or place.
The movement of the moving object, e.g. in the x- and y-direction, can be achieved by driving means such as electromagnetic, electrostatic or capacitance elements. For that, coils, electric and dielectric materials can be arranged properly as it is well known by a skilled person. Also possible and easy to implement are airflow means, like jets or fans.
It is favorable that the movement of the moving object by the driving means can be initiated by a single pulse stimulation, because then a longer distance can be covered whilst by periodic stimulation short distances can be covered. Furthermore, a stimulation in different directions can be applied, then the advantage occurs that a rotation of the moving object is achievable. By doing so, a precise motor can be created.
It proves as favorable for the nearly frictionless movement of the moving object, that the moving object only moves when a defined distance to the other object is provided. The air bearing between the first and second object can have different resonant frequencies. This is advantageous, because then several moving objects can be driven at different resonant frequencies which means at different times. An individual control of each second object is therewith possible. The thickness of the air bearing between the first and second objects can be varied by adapting the pressure between the objects. This permits a fine adjustment in the z-direction.